The lithium ion battery is a rechargeable cell with a very high energy density. The theoretical specific energy density of lithium-sulfur batteries is 2600 Wh/kg, which is one of the highest energy densities for batteries. Li—S batteries may become a successor of lithium-ion cells because of their higher energy density and the lower cost.
Elemental sulfur is a promising cathode material with high theoretical specific capacity and specific energy density for rechargeable lithium battery. However, sulfur cannot be solely used as the cathode material in Li—S batteries due to its high electrical resistivity and the high solubility of polysulfides in organic electrolyte solutions, resulting in a low utilization of the active material, a low coulombic efficiency, and a short cycle life of the sulfur electrode.
An international patent application No. PCT/CN2011/073598 discloses a cathode material for Li—S battery and method for forming the same. The cathode material comprises an acrylonitrile based polymer, sulfur and graphene. The international patent application also presents a method for preparing a cathode material for Li—S battery, including: dispersing 10-30 parts by weight of acrylonitrile based polymer in 30-1000 parts by weight of water, adding 0.1-5 parts by weight of graphene, adding 20-200 parts by weight of sulfur to said mixture, and the thus obtained mixture of acrylonitrile based polymer/sulfur/graphene oxide is homogenized before being heated to a temperature of 200-400° C. under an inert atmosphere and kept at said temperature for 1-20 hours, so as to obtain a cathode material.
Another international patent application No. PCT/CN2010/077530 discloses a cathode material for Li—S battery. The cathode material for Li—S battery comprises a dehydrogenized acrylonitrile copolymer, sulfur and carbon nanotubes, wherein the weight percentages of these components are as below: 20%≦dehydrogenized acrylonitrile copolymer ≦70%, 20%≦sulfur≦80%, 0%≦carbon nanotubes≦20%. The international patent application also presents a method for preparing a cathode material for Li—S battery, including: mixing carbon nanotubes and acrylonitrile copolymer in a ball mill, wherein ethanol is used as a dispersant; adding sulfur into the ball mill and further mixing; drying the mixture under vacuum to remove ethanol; heat treating and dwelling the mixture under an inert atmosphere; and cooling at ambient temperature, so as to obtain a cathode material.
However, as shown in FIG. 1 of the international patent application No. PCT/CN2010/077530, it can be seen that the cathode material partial is irregular particle. In order to get high coverage electrode film, there is a need for the material having a better particle morphology and an easy formation of the electrode film with a higher density to further improve the industrialization of the Li—S battery.